Pallade Veneta - One dead, 48 injured in unexplained Johannesburg blast

The explosion blew a hole in the road and gouged out cracks, skittling pedestrians and cars.

"(In the) early hours of this morning, we managed to recover a body of a male person on site where the explosion occurred," Emergency Management Services spokesman Robert Mulaudzi said.

Panyaza Lesufi, the premier of Johannesburg's Gauteng province, told a media briefing that 48 people were injured.

Witnesses reported chemical odours and escaping vapours after the powerful blast, which overturned vehicles, including minibus taxis.

Lesufi said a preliminary inspection did not reveal the cause of the explosion.

Experts are "still searching for the source," he said.

The blast occurred on a broad four-lane avenue used as a commuting artery by minibuses, bordered by high-rise buildings housing apartments and street-level stores.

Terrified people ran for safety after the blast, CCTV footage showed.

The area remained closed on Thursday as police chased away onlookers.

"It's about keeping this scene sterile," said Elias Mawela, the provincial police commissioner. "Should we have a secondary explosion, then we may lose lives".

Emergency services initially blamed underground gas pipes for the blast but the city's privatised gas company, Egoli Gas, said it was "unlikely" this was the case as customers were still receiving their supplies uninterrupted.

However, it issued a further statement after an initial inspection, saying that "one or two manhole covers" had been blown off and a "white gas-like substance" was seen coming out of these openings.

The city's mayor told reporters that homeless people around the area, who often sleep rough on the pavements overnight, had been moved to temporary shelters.

R.Lagomarsino--PV